Using two electrode voltage clamps, we investigated the effects of lidocaine on one type of glutamate transporter, EAAT3, and the role of protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI3K) in mediating the lidocaine effects. EAAT3 was expressed in Xenopus oocytes, and membrane currents were recorded after the application of L-glutamate (30 microM). Lidocaine increased glutamate-induced inward currents significantly at 2 concentrations (100 microM and 1 mM), but not at other concentrations. Lidocaine (100 microM) significantly increased the V(max), but not the K(m), of EAAT3 for glutamate compared with control. The action sites of lidocaine on EAAT3 seem to be intracellular, because only intracellularly injected QX314 (permanently charged lidocaine analog) increased the response. The combination of phorbol-12-myrisate-13-acetate, an activator of PKC, and lidocaine did not further increase the responses compared with phorbol-12-myrisate-13-acetate or lidocaine alone, although each of these three groups showed significantly bigger responses than controls. Three PKC inhibitors (staurosporine, calphostin C, and chelerythrine) did not affect the basal EAAT3 activity but abolished lidocaine-enhanced EAAT3 activity. Wortmannin (a specific PI3K inhibitor) inhibited EAAT3 basal activity and lidocaine-enhanced EAAT3 activity. Our results suggest that lidocaine enhances EAAT3 activity at certain concentrations and that PKC and PI3K may mediate these lidocaine effects.
Implications: By using the Xenopus oocyte expression system, we investigated the effects of lidocaine on a glutamate transporter (EAAT3). Our findings suggest that lidocaine enhances EAAT3 activity at certain concentrations and that protein kinase C and phosphatidylinositol 3-kinase may mediate these lidocaine effects.